Class 8 Science Question Answers - Stars and the Solar System (Old Syllabus)

Q1: What do you mean by celestial objects. Explain with examples?

Ans: The stars the planets and many other objects in the sky are called celestial objects. For example: moon, nine planets, asteroids etc.
Q2: Why phases of the moon occur?

Ans: Just like Earth, half of the moon is lit by the sun, and half is in shadow at any given time. As the moon travels around the Earth, we see the moon from different angles, and thus can see different percentages of light and shadow. When the moon is full, the moon is on the opposite side of the Earth from the sun. As a result, we can see the whole of the lit side of the moon. At new moon, exactly the opposite alignment exists, with the moon being between the Earth and the sun. At that point, we can only observe the shadowed side of the moon. At first and third quarter moons, the moon is at a 90 degree angle from the Earth and sun.
Q3: Why can't we hear any kind of sound on moon?

Ans: Moon has no atmosphere and as we know sound cannot travel when there is no medium thus we cannot hear any kind of sound on the moon.

Q4: Define the following:

1. Moon
2. Stars

Ans:
a. Moon: Moon is a celestial object that does not have its own sunlight; it is visible to us due to reflected sunlight. There is no atmosphere and water on the moon, its surface is dusty and barren. Moon revolves around the earth so it is also called the natural satellite of earth.

b. Stars: Stars are other celestial object that can be seen in the night sky. Sun is the nearest star from the Earth; the stars are millions of times farther than the sun, STARS are present in the sky during the day time also but because of the bright sunlight they are not visible to us. They appear to move from east to west in the sky.
Q5: Differentiate between planet and stars.

Ans: 

Q6: Differentiate between moon and stars.

Ans: A moon is simply a natural satellite that moves around a planet, tied gravitationally to its parent planet. But a star is a large mass of gas that generates energy due to the thermonuclear fusion reactions happening at their cores. They range in size from a few kilometres in diameter to several times larger than the solar system. They form large collections that make up star clusters and galaxies.
Q7: Name the person who landed on the moon for the first time along with the date at which he landed there for the first time.

Ans: On July 21, 1969 the American astronaut, Neil Armstrong landed on the moon for the first time.
Q8: Write some characteristics of stars.
Ans: Some characterstics of stars are as follows:
1. Have their own light.

2. Twinkles at night.

3. Since the stars are very far away, the telescope can only make them look brighter but not larger

4. A star has very high temperature.

5. There are billions of stars in the celestial sphere
Q9: Why we are not able to see the stars during the day time?

Ans: We are not able to see the stars during the day time because of the bright sunlight.
Q10: Why stars appear to move from east to west?

Ans: Earth rotates on its axis from west to east, thus stars appear to move from east to west.
Q11: Define constellation along with some examples.

Ans: Group of stars having a recognisable shape is called constellation. Constellation is an internationally defined area of celestial sphere. For example: Ursa Major, Orion etc.

Q12: Wright short notes on

1. Ursa Major
2. Orion

Ans: Ursa Major: Ursa Major can be seen in the sky during summer time in the early part of the night, it is also known as Big Dipper or Saptarashi. There are seven prominent stars in this constellation; it appears like a big question mark or ladle.
Orion: Orion can be seen in the sky during winter in the late evenings. It has seven or eight stars. The brightest star Sirius is located close to the Orion.
Q13: What is Cassiopeia?

Ans: Cassiopeia: Cassiopeia is a constellation that can be seen in the northern sky. It is visible during winter in the early part of night. It looks like distorted letter W or M.
Q14: Explain why planets do not collide while revolving around the Sun?

Ans: Planets move in their own orbit, thus they do not collide while revolving around sun.
Q15: What do you mean by satellite? Name some satellites.

Ans: Any celestial body revolving around another celestial body is called its satellite. Aryabhatta, INSAT, IRS, EDUSAT, Kalpana- 1, etc. are some satellites.
Q16: Differentiate between artificial and natural satellites?

Ans: Natural satellites are celestial body that orbits a planet or any other celestial body, they are found by nature. The most well-known natural satellite is the moon. The natural satellites are made up of natural materials like rocks, minerals, water, dust etc. The natural satellite cannot communicate on earth or with other planets. But artificial satellite is the device placed in orbit around the Earth, moon or other planet. They are man-made. The first artificial satellite was sputnik I. It can communicate with instruments on earth.
Q17: What are the uses of artificial satellites?

Ans: The artificial planet can communicate with instruments on earth. Artificial satellites have many uses, including relaying communication signals, making accurate surveys and inventories of the earth's surface and weather patterns, and carrying out scientific experiments.

Q18: Write short notes on following:

1. Mercury
2. Venus

Ans:

1. Mercury: It is the nearest planet to the sun. It is the smallest planet of our solar system. It is very close to the sun so it is quite difficult to observe it. It has no satellite of its own.Venus: 
2. Venus: It is the Earth's nearest planetary neighbour. It is the brightest planet in the night sky. Sometimes it appears in the eastern sky before the sunrise, and sometimes in western sky just after the sunset. Thus it is also called morning or evening star. It has no satellite of its own.

Q19: Write short notes on the following:

1. Jupiter
2. Saturn

Ans:

1. Jupiter: It is the largest planet of the solar system. It rotates very rapidly on its axis. It has a large number of satellites. It also has a faint ring around it.
2. Saturn: Saturn lies beyond Jupiter; it contains beautiful rings around it which is not visible with the naked eye. It has a large number of satellites. It is least dense among all planets.

Q20: Write short notes on the outermost planet of the solar system.

Ans: Outermost planet of solar system includes planets like Jupiter, Saturn, Uranus and Neptune. 

Jupiter: It is the largest planet of the solar system. It rotates very rapidly on its axis. It has a large number of satellites. It also has a faint ring around it.

Saturn: Saturn lies beyond Jupiter; it contains beautiful rings around it which is not visible with the naked eye. It has a large number of satellites. It is least dense among all planets.

Uranus: It can be seen via telescope only. In its orbital motion it appears to roll on its side. It rotates from west to east.

Neptune: It can be seen via telescope only. Neptune has a planetary ring system, though one much less substantial than that of Saturn.
Q21: Define asteroids.

Ans: Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones.
Q22: Define meteors and meteorites.

Ans: Small pieces of space debris (usually parts of comets or asteroids) that are on a collision course with the Earth are called meteoroids. When meteoroids enter the Earth's atmosphere they are called meteors. Most meteors burn up in the atmosphere, but if they survive the frictional heating strike the surface of the Earth and they are called meteorites.
Q23: Explain how you can locate pole star with the help of Ursa Major.

Ans: Yes. Pole Star is located by Ursa Major. On a clear moonless sky during summer at 9.00 p.m. at the northern part of sky we can see Ursa Major. Imagine a straight line that passes through these stars and extend this line towards the northern side to a star that is not too bright. This is a Pole Star. This star does not move at all. Ursa Major moves east to west of this Pole Star.
Q24: Why is the distance between stars expressed in light years?

Ans: Stars are very far from the earth, their distance if written in km will not be convenient to read and memorise, and thus large distances are expressed in light year. It is the distance travelled by light in one year.
Q25: What do you understand by the statement that the star is six light year away from the earth?
Ans. Stars are millions of kilometres away from the earth. It is not convenient to express such a large distance in the units of km. So the distance of stars from the earth is expressed in time taken by light to travel in one year. Six light years means time taken by light to travel in six years. 

Q26: What are the superstitious about the comets?

Ans: Superstitious about comets is that comets are messengers of disasters, such as wars, epidemics and floods, but it is actually a myth as appearance of comets is a natural phenomenon.

Q. 27. What are celestial bodies?
Ans. The stars, the planets, the moon and many other objects in the sky are called celestial bodies. 

Q. 28. Define phases of the moon.
Ans. The various shapes of the bright part of the moon as seen during a month are called phases of the moon. 

Q. 29. Why do we see only the part of the moon?
Ans. We see only that part of the moon from which the light of the sun is reflected towards us. So we see only the part of the moon.

Q. 30. Why does the size of the moon decrease every day after the full moon day?
Ans. After the full moon day the sunlit part of the moon visible from the earth decreases in size every day.

Q. 31. Why do we classify the sun as a star?
Ans. The sun is a star because it has its own source of energy and continuously emits heat and light. 

Q. 32. Why are stars invisible during the day time?
Ans. Stars are far away from us compared to the sun. So the glare of the sun is much more than the glare of star during the daytime. Therefore stars are not visible during the day time. 

Q. 33. What are planets?
Ans. The celestial bodies which revolve around the sun are called planets. There are eight planets in the solar system. 

Q. 34. Why do stars twinkle but planets not?
Ans. The stars are very far away from the earth. The point position of the stars vibrate to disturbance by air currents and hence they appear to twinkle. The planets are much nearer than of stars and they do not have disturbance by air current, so they do not twinkle. 

Q. 35. Define orbit.
Ans. A planet has a definite path in which it revolves around the sun. This path is called orbit. 

Q . 36. What are Asteroids?
 Ans. There is a large gap between the orbit of Mars and Jupiter. This gap is occupied by a large number of small objects that revolve around the sun. These are called asteroids.

Q . 37. What is meteor?
Ans. At night, when the sky is clear and moon is not there, sometimes bright streaks of light may be seen in the sky. This is called meteor. 

Q . 38. What are meteorites?
Ans. Some meteors are so large that they do not completely evaporate before reaching the earth. These are called meteorites. 

Q . 39. What is artificial satellite?
Ans. A man made satellite which is orbiting the earth is called artificial satellite.

Q . 40. What are comets?
Ans. Comets are the members of our solar system. They revolve around the sun in highly elliptical orbit as a bright head with a long tail.